: An extensive literature suggests that speed and accuracy of detection of a target object in an array of other objects (distractors) is a function of the locations of target and distractor objects and the visual and semantic characteristics of these objects. Recent evidence for control subjects and patients with frontal and parietal lesions suggests that response factors (such as whether the task requires a button press or target-touch response) may also critically influence performance on such tasks. On the basis of such data, as well as findings from physiological studies, we have developed a provisional model of the role of distinct fronto-parietal processing modules in location coding and "selection for action". This model predicts differing roles for spatial, object, and response factors in selection as a function of the integrity of each of the proposed processing modules. A major goal of this research program is to test whether the predictions of the model are borne out in the performance of patients with perceptual neglect, directional hypokinesic neglect, and optic ataxia, whose lesions are hypothesized to affect different modules. The proposed experimental program will center upon selective reaching tasks, and will culminate in a series of studies of real-object detection and prehension designed to have greater relevance to naturalistic action than do most traditional laboratory studies of visual attention. In addition to contributing to the understanding of normal and disordered percept-motor processing, data from these studies are expected to provide evidence bearing on the real-life action performance of patients with such disorders, and thus, to have clinical implications for assessment and treatment.